1. Field of the Invention
The present invention relates to a fluid actuated working cylinder having a cam driven by a piston via a flexible tension member. More specifically, this invention relates to a compact working cylinder which utilizes spring loaded deflection elements to maintain constant tension on the tension member.
2. Description of the Prior Art
The prior art is characterized by working cylinders shown in West German Patent No. 28 30 058, U.K. Patent Application 2 051 957 and U.S. Pat. No. 4,472,981. A working cylinder is generally constructed of a cylinder having a two faced piston slidably mounted therein, a cam or other sliding element mounted exterior to the cylinder, and a tensioning member connecting the two elements. A cylinder of this type is utilized to replace a piston and piston rod device because of its generally smaller size, in applications where such size is critical.
The cylinder is generally designed such that a chamber is formed on either side of the piston in the cylinder. The two chambers may be selectively pressurized to move the piston along the longitudinal axis of the cylinder. Movement of the piston thus results in equal movement of the cam on the exterior of the device because of the interconnection therebetween of the tensioning member.
Peter, U.S. Pat. No. 4,472,981 discloses a system in which the piston is mounted within the cylinder and the cam is adapted to be displaced by an inelastic tensioning member. The cam is suspended from the tensioning member and runs longitudinally along the exterior of the cylinder. The primary focus of the reference is the use of springs in the cam member, where the tensioning member is affixed. During operation, the piston and cam are repeatedly and quickly displaced. This rapid and sudden movement tends to wear the rollers and tensioning belts quickly. Springs are utilized to connect the ends of the tensioning belts to the cam, and are adapted to absorb some of the shock of a rapid movement or change of direction of the cam and piston.
During operation of any of the working cylinders, changes in the length of the tensioning member, or deviations in the length of replacement tensioning members is encountered. Additionally, mounting of the tensioning member is time consuming and difficult if the rollers must be permanently adjusted to tension the belt. The relatively small displacement of the springs does not allow for large tension in the tensioning members, nor will it compensate for anything but the smallest of deviations in the length of the tensioning member. Finally, the exterior mounting of the cam and its suspension or support from the tensioning member increase the chances of damage or interference with the movement of the cam.
United Kingdom Application 2 051 957 discloses a device utilizing two interconnected parallel cylinders, one of which is smaller than the other. A piston is mounted in each cylinder, and both are connected by tensioning members from each face to the corresponding face of the other piston. This device thus creates two pressure chambers, formed by the two pistons, one on each set of piston faces. The tensioning members are passed from one cylinder to the other and reverse direction therebetween by being passed over a pulley. The pulleys are connected to shafts which extend outside the cylinder housing and translate the movement of the pistons to other forms. The shafts themselves may be utilized for angular displacement, or pulleys may be mounted thereon with belts mounted across the exterior pulleys to achieve linear displacement in proportion to the movement of the internal pistons and tensioning members.
This device utilizes a self-tensioning system in one embodiment, in which one of the shafts is mounted in a cylinder head which is moveable with relation to the main cylinder housing. The cylinder head is held in position by a plurality of spring loaded studs, which urge the cylinder head away from the main cylinder housing. In this fashion, tension is maintained on both the internal tensioning members and the outer belts, as the shaft about which they are mounted is displaced away from the second, immobile shaft. This device, while providing for tensioning of the tensioning members and external belts, suffers from the same detrimental characteristics as the device described in U.S. Pat. No. 4,472,981. The exterior mounting of the linear motion belts allows for damage or interference with the motion of the device. Similarly, the size of the device is increased by the space required for external pulleys and belts.
Lastly, West German Patent No. 28 30 058 describes a working cylinder having deflection pulleys located in the end areas of the cylinder housing. Each deflector pulley is positioned on an axle that is mounted transverse to the longitudinal axis of the cylinder housing and serves as support for the deflector pulley. Spring-loaded devices are provided which apply loading to the axle in a direction away from the cylinder, so that the tension member is under constant tension.
The disadvantage of this working cylinder is, like the other devices described above, the particular arrangement of the deflector pulleys on the working cylinder. These pulleys are very bulky in design and require considerable space. What is lacking in the art, therefore, is a working cylinder which provides a self-tensioning feature, but is at the same time compact and resistant to external interference with its operation.